This invention relates to well logging and more particularly to a well logging system incorporating fiber optic well logging cable for use in boreholes.
Requirements in modern well logging systems for extremely wide bandwidths on the order of tens of megahertz have caused the introduction of well logging cables having outer armour and employing several electrical conductors disposed within the armour in conjunction with one or more fiber optic components having extremely wide optical bandwidths for the transmission of data in both analog and digital form to and from a downhole tool.
The invention described in the present disclosure is directed to a feedthrough connector and more particularly, one which is able to support and join a divided optical fiber at an intersection point such as a well logging tool bulkhead. Establishing optical communication paths along optical fibers crossing pressure differential bulkheads can create problems similar to but significantly different from the problem of carrying electrical conductors through such bulkheads. Examples of prior art feedthrough connectors are shown in U.S. Pat. No. 4,593,970 and 4,607,911 and 4,891,640 which is assigned to the assignee of the present invention. One particular difference between the passage of an optical fiber from an electrical conductor through a bulkhead is that the optical fiber must be supported in some fashion to maintain its optical integrity without exerting undue bending forces on the fiber. In well borehole usage, however, the optical fiber must be used repeatedly in hostile enviromental circumstances. It may carry optical signals representing data from an ambient atmospheric pressure through a wall or bulkhead into a extremely high pressure, high temperature environment. It is not uncommon to encounter temperatures as high as 400.degree. C. to 500.degree. F. and ambient pressures up to 25,000 psi in well boreholes. Whatever the circumstances, the optical fiber typically must communicated an optical path through an opening formed in a bulkhead so that it can provide means for communicating high data rate data a cross a bulkhead in a pressure isolated well logging tool which is lowered into the well.
The data output of a modern well logging tool can be so great as to require the bandwith of an optical fiber to deliver the data from the logging tool to the surface. When the optical fiber passes through a bulkheat, it must have a tight pressure seal formed around it by the feedthrough and yet must be optically transparent enough so that light signals are transmitted along the fiber or through the junction of two fibers. Pressure leakage from one environment to another is prevented by the optical feedthrough connector of the present invention. Moreover, this feedthrough should have a mechanism which enables it to be mounted on the supporting bulkhead or frame member for a quick disconnection, if desired, when it is necessary to remove the logging cable from the tool, for example. In this regard, the optical feedthrough according to the concepts of the present invention includes a structure which mechanically attaches to the supportive substructure without inflicting additional stress on the optical fiber and maintains alignment of the optical fiber at the junction of its severance in such a manner as to provide a continuous optical path across the junction. Moreover, the structure of the present invention provides a device for this purpose which is quickly separable and which is able to secure the optical fiber in passage through a bulkhead in a fluid tight manner without undue forces impinging on the optical fiber.
While these advantages are important advantages, there are additional benefits obtained through the apparatus of the present invention. The device can be installed and located at a particular location on a well logging instrument in a manner such that the optical fibers forms a continuous path of optical nature through a pressure differential bulkhead and aligns and supports the optical fiber from the well logging cable to the interior of the down hole instrument package.